Although a number of different kinds of coating materials are layered on one another in most cases of painting vehicles such as automobiles and electric appliances and the like, the coating material to be applied to the topmost surface of the paint surface on automobiles is required to protect the undercoating and design features such as gloss etc. However, if a product painted with such a coating material has been used for a long period of time, the coated surface may be damaged for various reasons, for example with automobiles, in cases where stones or sand contact the coated surface forming scratches called chipping, cases where the coated surface is scratched by the brushes of automatic car-washing machines, and cases where keys inadvertently contact the coated surface when locking the door. The appearance of the coated surface is deteriorated, due to such scratches. Further, the scratches may adversely affect the coated surface of the undercoatings and the like. Therefore, the coating material painted on the topmost painted surface must have abrasion resistance.
In order to impart the effect of abrasion resistance, selecting appropriate kinds of resins, blending ratios and the like is most frequently carried out. Specifically, a method of imparting abrasion resistance by hardening the coating film is known. However, once a hard coating film is scratched, problems such as cracking occur. And so, coating films having satisfactory abrasion resistance have not been obtained. On the other hand, the technical means to form a soft coating film where fine scratches can be naturally restored to the original state, due to its elasticity have been known. However, there are problems in that large scratches in the soft coating film, which cannot be restored occur easily and the soft coating film is stained easily as well.
Therefore, it has been attempted to increase the abrasion resistance of coating film by adding to a coating material an additive which increases abrasion resistance (for example, see Patent publications 1 and 2). The additive used is fine particles of silica and the like. If the fine particles are added to the coating film, the resulting coating film becomes hard and scratch-resistant. However, the level of abrasion resistance is not satisfactory and there is the problem that some of the fine particles are unstable in the coating material.